1. Field of the Invention
The present invention relates to a novel fluorine-containing non-crystalline copolymer with good oil resistance, heat resistance and low temperature properties, and more particularly, the present invention relates to a novel fluorine-containing non-crystalline copolymer comprising repeating units derived from tetrafluoroethylene and a fluorovinyl ether of the formula: EQU CH.sub.2 .dbd.CHOCH.sub.2 (CF.sub.2).sub.n X (I)
wherein X is halogen or hydrogen and n is a number of 2 to 8 and optionally repeating units derived from vinylidene fluoride or ethylene.
2. Description of the Related Art
Hitherto, a copolymer of vinylidene fluoride and hexafluoropropylene and a terpolymer of vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene are used in various fields in the form of a packing, diaphragm or hose since they are fluoroelastomers with good heat resistance, oil resistance and chemical resistance.
When these copolymers are used in applications where they contact with alkalis or amines, or motor oils, they are attacked by such chemicals and become brittle and sometimes lose their functions as a rubber.
As a fluorine-containing elastic copolymer which has good resistance to the alkalis, amines and various oils, a copolymer of tetrafluoroethylene and perfluoro(vinyl ether), a copolymer of ethylene and perfluoro(vinyl ether) and a terpolymer of tetrafluoroethylene, ethylene and perfluoro(vinyl ether) (cf. Japanese Patent Kokai Publication No. 15212/1987) or a copolymer of tetrafluoroethylene and propylene are proposed. However, a copolymer comprising perfluoro(vinyl ether) is an expensive elastomeric copolymer since the synthesis of perfluoro(vinyl ether) is complicated. Thus such as copolymer does not satisfy the requirements of the practical use.
The copolymer of tetrafluoroethylene and propylene has unsatisfactory oil resistance since it contains a comparatively large amount of propylene, and it loses flexibility at low temperatures so that it cannot be used in an application which requires prolonged durability at low temperatures.